The present invention relates generally to an internal combustion engine rocker arm for controlling engine valves during positive power and engine braking. In particular, the present invention is directed to a rocker arm having a lost motion piston integrated into the rocker arm assembly.
Various embodiments of the present invention may have particular use in connection with a compression-release engine retarder for an internal combustion engine. Engine retarders of the compression release-type are designed to convert, at least temporarily, an internal combustion engine of compression-ignition type into an air compressor. In doing so, the engine develops retarding horsepower to help slow the vehicle down. This can provide the operator increased control over the vehicle and substantially reduce wear on the service brakes of the vehicle. A properly designed and adjusted compression release-type engine retarder can develop retarding horsepower that is a substantial portion of the operating horsepower developed by the engine in positive power.
The basic design for a compression release engine retarding system of the type involved with this invention is disclosed in Cummins, U.S. Pat. No. 3,220,392, issued November 1965. The compression release-type engine retarder disclosed in the Cummins ""392 patent employs a hydraulic system or linkage. The hydraulic linkage of a typical compression release-type engine retarder may be linked to the valve train of the engine. When the engine is under positive power, the hydraulic linkage may be disabled from providing valve actuation. When compression release-type retarding is desired, the hydraulic linkage is enabled such that valve actuation is provided by the hydraulic linkage responsive to an input from the valve train.
Among the hydraulic linkages that have been employed to control valve actuation (both in braking and positive power), are so-called xe2x80x9clost-motionxe2x80x9d systems. Lost-motion, per se, is not new. It has been known that lost-motion systems are useful for valve control for internal combustion engines for decades. In general, lost-motion systems work by modifying the hydraulic or mechanical circuit connecting the actuator (typically the cam shaft) and the valve stem to change the length of that circuit and lose a portion or all of the cam actuated motion that would otherwise be delivered to the valve stem to actuate a valve opening event. In this way lost-motion systems may be used to vary valve event timing, duration, and the valve lift.
In conventional compression-release retarding or braking systems, the system is a bolt-on accessory that fits above the overhead. In order to provide space for mounting the braking system, a spacer may be positioned between the cylinder head and the valve cover which is bolted to the spacer. This arrangement may add unnecessary height, weight, and costs to the engine. Many of the above-noted problems result from viewing the braking system as an accessory to the engine rather than as part of the engine itself.
As the market for compression release-type engine retarders has developed and matured, manufacturers of these retarders have been requested to design systems that secure higher retarding horsepower; increase the air mass delivered to the engine cylinders for the compression-release event; reduce the weight, size and cost of such retarding systems; and improve the inter-relation of various collateral or ancillary equipment, such as silencers, turbochargers and exhaust brakes with the retarding system. In addition, the market for compression release engine retarders has moved from the after-market, to original equipment manufacturers. Engine manufacturers have shown an increased willingness to make design modifications to their engines that would increase the performance and reliability and broaden the operating parameters of the compression release-type engine retarder.
One possible answer to engine manufacturers"" demands has been to integrate components of the braking system into existing engine components. One attempt at integrating parts of the compression braking system into the engine is found in U.S. Pat. No. 3,367,312 to Jonsson, which discloses an engine braking system including a rocker arm having a plunger, or slave piston, positioned in a cylinder integrally formed in one end of the rocker arm wherein the plunger can be locked in an outer position by hydraulic pressure to permit braking system operation. Jonsson also discloses a spring for biasing the plunger outward from the cylinder into continuous contact with the exhaust valve to permit the cam-actuated rocker lever to operate the exhaust valve in both the power and braking modes. In addition, a control valve is used to control the flow of pressurized fluid to the rocker arm cylinder so as to permit selective switching between braking operation and normal power operation. However, the control valve unit is positioned separately from the rocker arm assembly, resulting in unnecessarily long fluid delivery passages and a longer response time. This also leads to an unnecessarily large amount of oil that must be compressed before activation of the braking system can occur, resulting in less control over the timing of the compression braking event.
Consequently, there is a need for a simple, yet effective braking system which incorporates the control valve for a lost motion piston integrated into a rocker arm. The integration of the control valve into the rocker arm assembly shortens the hydraulic passages used, improves response time, and may improve compliance.
Another problem facing engine brake manufacturers arises from the use of a unitary cam to drive a rocker for both main event and braking events. Use of a unitary cam may present a significant risk of valve-to-piston contact. Use of a unitary cam for both events, such as is disclosed in U.S. Pat. No. 3,809,033 to Cartledge, means that the extension of the lost motion piston required for the engine braking event will be added to the relatively large main exhaust lobe motion. Because the lash between the lost motion piston must be eliminated to carry out the braking event, the main valve event motion may produce a greater than desired main exhaust event during engine braking, potentially causing valve to piston contact.
Accordingly, there is a need for a system and method that avoids the occurrence of valve-to-piston contact when a unitary cam lobe is used to impart the valve motion for both a compression release event and a main exhaust valve event. More particularly, there is a need for a system and method of limiting the stroke or displacement of a lost motion piston when a lost motion system is imparted with the motion from a main exhaust cam lobe.
One way of avoiding valve-to-piston contact as a result of using a unitary cam for both compression release valve events and main valve events is to limit the motion of the lost motion piston which is responsible for pushing the valve into the cylinder during compression release braking. A device that may be used to limit slave piston motion is disclosed in U.S. Pat. No. 4,399,787 to Cavanagh. Another device that may be used to limit slave piston motion is disclosed in U.S. Pat. No. 5,201,290 to Hu. Both of these (reset valves and clip valves) may comprise means for blocking a passage in a lost motion piston during the downward movement of the lost motion piston.
Thus there is a need for a compression release-type braking system that both integrates the lost motion system into the engine rocker arm and includes a means for resetting or clipping the motion of the lost motion piston that is incorporated into the rocker arm.
It is also desirable to combine multiple profiles, bumps, or lobes on a single cam, e.g., a positive power or main event exhaust valve bump or motion, an engine brake bump or motion, a brake gas recirculation (BGR) bump or motion, and/or an exhaust gas recirculation (EGR) bump or motion. When this is done there must be a mechanism to select which profile(s)/bump(s) are to be active. Improved operation can be obtained if the main event motion is not altered by the addition of other motions.
Thus there is a need for an engine braking system that integrates the lost motion system into the engine rocker arm, includes resetting or clipping capability, and provides for the selection or de-selection of engine braking, BGR, and/or EGR bumps on a unitary cam used to actuate an engine valve.
Therefore, an advantage of some, but not necessarily all embodiments of the present invention is that they may provide a system and method for actuating an engine valve that incorporates a lost motion system into an engine rocker arm.
Additional advantages of embodiments of the present invention are set forth, in part, in the description which follows and, in part, will be apparent to one of ordinary skill in the art from the description and/or from the practice of the invention.
In response to this challenge, Applicants have developed an innovative rocker arm assembly for actuating an engine valve, said assembly comprising a rocker arm, a hydraulic circuit within the rocker arm, a lost motion piston extending out of the rocker arm and communicating with the hydraulic circuit, a check valve disposed in the hydraulic circuit, a reset piston disposed in the rocker arm and adapted to selectively open the check valve, and a control piston disposed in the rocker arm and adapted to selectively lock the reset piston.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed. The accompanying drawings, which are incorporated herein by reference, and which constitute a part of this specification, illustrate certain embodiments of the invention and, together with the detailed description, serve to explain the principles of the present invention.